The image on the right is the second master of a verbal font.
If kerning in the first master is negative and in the second master is zero, this breach occurs.
What version of Glyphs do you have? It should be fixed in the cutting edge version.
I use the latest update 2.6.2 (1237)
Does kerning in vb fonts have not yet been variable?
The kerning for the slant (second master) is vary
but in GX export, first master kerning apply to it